The present invention relates to an integrated digital x-ray diagnostic system and a method for conducting dental radiography which includes optimizing exposure settings based on certain physical parameters of a patient, communicating the operational status of the x-ray generator and the exposure settings directly to a CCD sensor without radiation sensitive detector elements, and supplying various viewing stations with image data thereby improving dental office workflow.
Digital image detectors, such as CCD sensors used in conventional video cameras, have been adapted to be x-ray sensitive elements in dental x-ray applications. For the past few decades, CCD sensors have been established as a leading technology in high-performance digital x-ray imaging. Unlike matrix-addressed sensors like amorphous silicon panels and CMOS imagers, CCD sensors read out their signal by transporting charge packets across their silicon substrate. The advantages of using a CCD sensor in conjunction with a typical digital x-ray diagnostic system often include high resolution and sensitivity, low noise and reduced radiation loads. Examples of inventions using CCD-type sensors in dental environments are described in U.S. Pat. Nos. 5,513,252, 5,784,429, and 6,002,742.
Methods and devices used for triggering the activation and/or deactivation of the x-ray generator used in connection with a CCD sensor vary widely in the art. Generally, most dental x-ray diagnostic systems used today incorporate sensing elements disposed in or around the CCD image sensor. These configurations allowed companies to manufacture just the x-ray sensing components of the system, and then sell those components to dentists, who would then combine them with x-ray generation units already installed in the dental offices. Such a componentized approach reduced the cost of the new equipment and therefore may have facilitated the overall industry shift from film-based radiography to digital diagnostics. It has also, however, led to significant technical limitations in the art.
In one known arrangement, one or more supplementary x-ray sensing elements are located close to the imaging area to detect the start and end of the x-ray pulse. Such an arrangement is disclosed in Crosetto, et al, U.S. Pat. No. 5,331,166. A signal is sent from the supplementary sensing element to the control circuitry of the image sensor to control image acquisition. The use of supplementary sensing elements adds size and complexity to the image sensor arrangement. The supplementary sensing elements also have to cover a significant part of the image area to minimize the risk of being shaded by a dense part of the object to be imaged.
In another arrangement, Sayag, et al., U.S. Pat. No. 5,510,623, the image sensor itself is continuously read out while waiting for exposure. The signal, either from one pixel or summed from many pixels, is compared to a fixed or variable threshold to determine the onset of radiation. This method as used with, for example, CCD sensors, requires shifting of the image along the sensor. The disadvantage of this method is the need of precise amplitude and timing for the shifting clocks in order to avoid loss of signal and image smearing.
Nelvig, U.S. Pat. No. 6,002,742, describes an arrangement where, in one embodiment, in-coming radiation is sensed by the use of several sensing diodes positioned at the back of the CCD device. Once radiation is sensed, the x-ray source is triggered to deactivate. In another embodiment, the CCD itself acts as the sensing medium by utilizing a multitude of charging pixel capacitors within the CCD device itself. However, both Nelvig embodiments require clocking the CCD cell by a logic device to determine the length and dose of the radiation. Additionally, both embodiments do not utilize customized exposure times calculated based on varying categories of teeth (i.e. incisors, canines, pre-molars and molars), and most importantly, varying anatomies of the patient (adult or child). This lack of tailored exposure settings may increase the risk of over-exposing children.
Schick, et al., U.S. Pat. No. 5,912,942, and Schick et al., U.S. Pat. No. 6,069,935, a continuation of the former, describe an x-ray detector with a scintillator that converts the x-ray energy into an electrical signal by using CMOS active pixel array sensor. Using CMOS sensors allows simple, low cost and low power solutions. The main disadvantages are the lower dynamic range, high pattern noise, lower resolution, high dark current and fair quantum efficiency compared with the CCD image sensors.
Finally, all of the above arrangements require the CCD to be in a perpetual charged state because they are in constant anticipation of incoming radiation. The charged CCDs lead to heightened noise accumulation along an unregulated exposure integration cycle, which detrimentally affects the quality of the resultant image.
Methods for displaying digital images after they have been captured have also taken many forms in the known art. Generally, a personal computer electronically attached to the image sensor itself or to an image processing unit is the most commonly employed technique in the art. Typically, a display computer is placed in a separate office where it can be manipulated away from the x-ray source so as to limit the amount of radiation exposure experienced by dental office employees. There are also provisions for presenting images on a display located adjacent a dentist's chair, facilitating viewing of the captured x-ray image(s) by doctor and patient alike. This arrangement typically involves an additional presentation/processing unit, as indicated above, located out of range of the x-ray source. However, there are obvious drawbacks in having stationary and remote display arrangements, the most evident being the disruption in the efficiency of dental office workflow. Before an image can be viable for diagnosis, or in the latter case, presented to a patient, the image must be digitally manipulated for precision, clarity and resolution. As a consequence, the x-ray technician is forced to take several additional steps in obtaining an adequate image. Generally, the technician first activates the x-ray source from a control room usually outfitted with radiation attenuating materials. A display unit, depending on the individual office configuration, may or may not be situated in the same x-ray control room. In any case, the technician is forced to leave the control post, operate the display unit, usually a personal computer, and retrieve and adjust the digital image. In many instances, however, the first take does not suffice, requiring the technician to repeat the procedure until a usable image is obtained. This process leads to inefficiencies and decreased productivity in the dental office, as well as increased exposure of patients to x-radiation.
Therefore, a need exists for a practical digital x-ray system and method of application in which radiation sensing elements disposed in or about a CCD sensor are no longer required. A need also exists for a system and method of obtaining dental radiographs without exposing young patients to superfluous radiation. Finally, a need exists for a system and method for providing technicians with the ability to capture, view, and manipulate digital radiographs without having to leave their post.